Descriptions

Chum salmon from different stocks were bred together in two experiments. Three stocks contributed gametes to one experiment, two stocks to another. Sibling groups of eggs, alevins, and fry were maintained in a common environment. Variability of development rates, rearing performance, susceptibility to disease, and behavioral traits was partitioned into genetic and non-genetic components. Embryonic development rate differed among the progeny of sires in crossbred groups. Its heritability was high in crossbred but not in purebred groups, and was correlated with geographical location of parental stocks and size of eggs. Size after rearing was affected by sires within parental groups indicating that its heritability is significant. It was also affected by egg size and geographical location of parental stock. Susceptibility to the marine disease vibriosis in controlled and natural challenges differed among sires within parental stocks. It is probably heritable in these stocks. Behavioral response to a salinity gradient, and length of residence in a stream were not affected by sires or parental stocks. Evidence for interactive effects was lacking for all traits. These observations lead to acceptance of the hypothesis that observed traits related to fitness (e.g., development rate) exhibit significant additive genetic variability in crossbred groups of salmon but not in purebred groups. Thus, the notion that crossbreeding may be advantageous cannot be excluded. A conceptual model is described for assessing selection in either a wild or hatchery stock. Dynamics are simulated for a stock in which (1) the number of returns per spawner depends on the number of spawners, (2) the number of returns is reduced biennially (simulating competition from pink salmon), and (3) age of maturation is 3 or 4 years. When age of maturation is given high heritability (h²=1) both average age and abundance cycle biennially; when heritability is low (h²=0) average age but not abundance cycles biennially. The first pattern has been reported for chum salmon in places where pink salmon spawn in significant numbers biennially. This result suggests that chum salmon, by genetic regulation of their age structure, can avoid competition with pink salmon.